The research project proposed here is designed to determine the precise chemical nature of the mineral calcium phosphate phase(s) and its three-dimensional structural relationship with the collagen fibrils in cementum. The proposed study will characterize these properties and devote considerable effort to understanding the chemical and structural changes as a function of tissue maturation and aging. Two primary extracellular components of cementum are inorganic. mineral solids and organic collagen fibrils, making up over 80 percent of the tissue mass. Chemical and structural changes of these components, which take place at the molecular level during tissue maturation, influence the quality of the tissue function (i.e., structural-mechanical support). Currently, there is very little information in the literature on the mineral composition and its relations to collagen in cementum as a function of aging. The delineation of these properties, and changes during aging and under pathological conditions, will provide critical information that will support the development of new clinical treatments and materials for periodontal diseases - an increasing health problem in the field of dentistry, particularly for the growing segment of the older population. The proposed study will make extensive use of (1) high-voltage electron microdiffraction/probe microanalysis for chemical analysis; (2) high-voltage stereomicroscopy and 3-D computer serial reconstruction for ultrastructural characterization: (3) for specimen preparation, anhydrous techniques and ultracryomicrotomy will be employed in order to circumvent mineral artifacts during preparation and analyses. These techniques represent the most powerful tools available today, and in combination should yield the most intimate knowledge of cementum minerals and collagen yet obtained.